The theory is that it causes deeper sleep, which = more REM cycles, which = more growth hormone output. Some studies have claimed that it increases natty test production, but no one seems to notice that effect.

Essentially people take it because they sleep better and there may or may not be additional benefits to it. It's a non habit forming sleeping aid that's cheap.

When I was taking it I started getting massive exertion headaches at the gym and I swear it messed with my sex drive. Sex drive may have been all in my head but yeah, for whatever reason it fucked me up in the gym.